Bi-phase (Scott-T) transformer double volted AC electrostatic coalescer

ABSTRACT

An electrostatic coalescer apparatus for separating water from a crude oil emulsion comprises a vessel housing having a cavity, an inlet for receiving a crude oil emulsion and outlets for water and purified crude oil. First and second pairs of electrodes are positioned in the vessel cavity. A first Scott-T transformer circuit is coupled to the first pair of electrodes and a second Scott-T transformer circuit is coupled to the second pair of electrodes. The first and second Scott-T transformer circuit receive as an input a 3-phase power supply and output a 2-phase high voltage signal pairs of electrodes. The 2-phase voltage generated between the first pair of electrodes is of the same amplitude and phase as the voltage generated between the second pair of electrodes via the respective Scott-T transformer circuits. A method comprises steps performed during operation of the apparatus.

FIELD OF THE DISCLOSURE

The present disclosure relates to chemical separation and moreparticularly relates to an apparatus for separating water from oil-watermixture by using Bi-phase (Scott-T) Transformers to transmit highvoltage electricity within a coalescer vessel in order to promotecoalescence and separation of water from the oil-water mixture.

BACKGROUND OF THE DISCLOSURE

In crude oil exploration and production, various fluid streams extractedcan contain impurities including appreciable amounts of water, salt andother undesirable constituents. So-called “upstream” processes aretherefore taken to remove the impurities, particularly water, from thefluid stream. Research into capabilities for removal of such impuritieshas increased in importance due to the possibility of exploitingdeposits that have been previously disposed of for containing too muchwater. Thus far, the two most common techniques for removal water is bygravitational separation and electrostatic coalescing. The gravitationaltechnique, which is the most common method, separates water from crudeoil by differences in their density. Typically, oil productionfacilities use gravity separators to remove most of the water associatedto the crude oil production. However, when the water is dispersed insmall or microscopic droplets in a continuous phase water/oil emulsion,gravitational separation does not work well, with the result that anappreciable amount of water tends to remain.

A more efficient technique for separating continuous phase emulsions isto remove the water electrostatically by passing the emulsion through anestablished electric field. One common apparatus to perform thisprocedure includes housing charged electrodes spaced apart within avessel known as an electrostatic coalescer. The coalescer typicallyincludes an emulsion inlet, an outlet for a lighter component (oil) andanother outlet for the heavier component (water). The electric fieldacts to augment the size of water droplets within the emulsion. Thelarger droplet can then be more efficiently separated by gravity fromthe oil and then removed from the vessel.

Certain conventional electrostatic designs use alternating current (AC)current transformers to transmit a high voltage to the electrodes housedwithin the vessel. The most frequently used configuration includes threesingle phase AC transformers installed on the vessel and connected tothe electrodes within the vessel through a high voltage entrancebushing. Typically, in a step-up transformer each single-phasetransformer is equipped with a single electrical coil of wire called the“primary winding” (lower voltage) and another called the “secondarywinding” (stepped up to higher voltage). Power is typically provided tothe primary winding via a three-phase power supply with two phasesconnected to each transformer (phase to phase, delta connection). Oneend of the secondary winding of each transformer is connected to theelectrodes while the other end of the secondary winding is grounded.

The conventional designs include three high voltage connections (onefrom each transformer) with the same voltage level and mutual phaseshifts (φ) of 120 degrees. Set of electrodes are connected to one of thethree transformers. This configuration generates electrostatic fieldswith same voltage intensity and phase shift (φ) of 120 degrees. However,the use of single-phase transformers in this design requiresnon-symmetrical sets of electrodes that generate unsynchronizedelectrostatic fields with phase shifts. This design configurationsuffers from inefficiencies in that the phase shifts of the AC fieldsare not optimal for water droplet aggregation and separation.Furthermore, the conventional design is subject to undesired voltagedrops and power losses.

SUMMARY OF THE DISCLOSURE

In a first aspect, the present disclosure describes an electrostaticcoalescer apparatus for separating water from a crude oil emulsion. Thecoalescer apparatus comprises a vessel housing having a cavity, an inletfor receiving a crude oil emulsion, at least one outlet for output waterremoved from the emulsion, and a further outlet for purified crude oil.The apparatus further comprises first and second pairs of electrodespositioned adjacently within the cavity of the vessel. A first Scott-Ttransformer circuit is coupled to the first pair of electrodes. Thefirst Scott-T transformer receives as an input a 3-phase power supplyand outputs a 2-phase high voltage signal to the first pair ofelectrodes. A second Scott-T transformer circuit is coupled to thesecond pair of electrodes. The second Scott-T transformer circuitreceives as an input a 3-phase power supply and outputs a 2-phase highvoltage signal to the second pair of electrodes. The 2-phase voltagegenerated between the first pair of electrodes by the first Scott-Ttransformer circuit is of a same amplitude and phase as a voltagegenerated between the second pair of electrodes by the second Scott-Ttransformer circuit.

In a preferred implementation, the electrodes in the first pair and theelectrodes in the second pair extend in a horizontal orientation.

In some embodiments, the first pair of electrodes includes an upperelectrode and a lower electrode. The upper electrode receives a signalfrom the first transformer circuit of a first phase and the lowerelectrode receives a signal from the first transformer circuit of asecond phase 90 degrees shifted with respect to the first phaseSimilarly, the second pair of electrodes includes an upper electrode anda lower electrode and the upper electrode and lower electrodes receivesignals from the second transformer circuit that are 90 degrees shiftedwith respect to each other.

The first and second Scott-T transformer circuit preferably each includea main transformer and a 86.6% (0.5×√3) ratio teaser transformer thattaps the main transformer in a 1:1 ratio. The main transformer includesa primary winding having a first end coupled to a one of the phases ofthe three-phase power supply, and a second end coupled to another of thephases of the three-phase power supply. The Main transformer center tapthen connects to one end of Teaser transformer while the other endconnects to the remaining phase. The main transformer includes asecondary winding having a first end coupled to a first one of theelectrodes of the first or second pairs of electrodes, and a second endcoupled to ground. In some implementations, the teaser transformerincludes a secondary winding having a first end coupled to a second oneof the electrodes of the first or second pairs of electrodes, and asecond end coupled to ground.

In certain embodiments, the voltage generated within first and secondpairs of electrodes is in a range of 15 Kilovolts to 25 Kilovolts.

In another aspect, the present disclosure describes a method removingwater and soluble impurities from a crude oil emulsion. The methodcomprises introducing the crude oil emulsion into an electrostaticcoalescer apparatus having a vessel with first and second pairs ofelectrodes, generating a homogenous bi-phase AC voltage signal betweenelectrodes of the first and second pairs of electrodes; wherein waterpresent in the emulsion aggregates and separates from the crude oilemulsion by exposure to the high voltage signal within the vessel, andremoving the aggregated water from the vessel of the apparatus.

In some implementations, the aggregated water drops by force of gravityto the bottom of the vessel and is removed from the vessel via outlets.

These and other aspects, features, and advantages can be appreciatedfrom the following description of certain embodiments and theaccompanying drawing figures and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram of a bi-phase transformer electrostaticcoalescer apparatus according to an embodiment of the presentdisclosure.

FIG. 1B is an enlarged view of a portion of FIG. 1A illustrating anexample configuration of a bi-phase Scott-T transformer employedaccording to the present disclosure.

FIG. 2A shows another view of the bi-phase coalescer apparatus shown inFIG. 1A illustrating a wave form of differential voltage between thesymmetric plates supplied by bi-phase phase transformers according to anembodiment of the present disclosure.

FIG. 2B is an exemplary graph of normalized grid's differential voltageover time generating an AC electric field that can be used in thebi-phase coalescer apparatus according to the present disclosure.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS OF THE DISCLOSURE

The present disclosure describes an electrostatic coalescer apparatusand associated method for separating water from water-in-oil mixturesthat uses bi-phase (Scott-T) transformers to step up voltage andtransmit high voltage electricity to the electrodes housed in thecoalescer apparatus. The Scott-T transformer is a transformer circuitthat is used to produce two-phase electric power, with a phase shift of90 degrees, from a three-phase source.

FIG. 1A is a schematic cross-sectional view an embodiment of anelectrostatic coalescer apparatus 100 according to the presentdisclosure. The coalescer is housed in a vessel 105 that defines acavity 110 and a longitudinal axis 112. The vessel 105 features anemulsion inlet 115 for receiving a crude oil emulsion that can containappreciable amounts of water, salt and other undesirable constituents.In some embodiments the emulsion inlet 115 is positioned at the bottomof the vessel 105 and the emulsion enters the vessel under positivepressure. The emulsion inlet can lead through an inlet header 116 thatconveys the input emulsion deeper into the vessel to avoid the presenceof accumulated water. At least one outlet for water is positioned at thevessel 105. In the embodiment shown in FIG. 1A, there are two such wateroutlets 120, 122. After water has been separated from the emulsion asdescribed further below, the water exits from the vessel via outlets120, 122 by force of gravity. The crude oil from which impurities havebeen removed exits from the vessel via a crude outlet 125 that can bepositioned, as shown, at the top of the vessel 105.

Within the vessel 105, two pairs of electrodes are positionedhorizontally adjacent to each other. The first pair of electrodesincludes electrodes 132 and 134 and the second pair of electrodesincludes electrodes 136 and 138. In the first pair electrodes 132 ispositioned above electrode 134. In the second pair electrode 136 ispositioned above electrode 138. All of the electrodes 132, 134, 136, 138extend horizontally (in the direction of the longitudinal axis 112). Insome embodiments each of the electrodes 132, 134, 136, 138 comprises alayer of charged grids. The first pair of electrodes 132/134 isconnected to a first bi-phase Scott-T transformer circuit 140. Thesecond pair of electrodes 136/138 is connected to a second bi-phaseScott-T transformer circuit 145. The coalescer apparatus 100 can beconsidered to be “double-volted” in that each electrode pair includestwo layers of grids that are connected to transformers. The pairs ofelectrodes 132/134, 136/138 are symmetrically positioned about a centerof the vessel (along the longitudinal axis 112). Together, theelectrodes cover approximately the entire length of the vessel.

In some embodiments, the first and second bi-phase Scott-T transformercircuits are equivalent. An enlarged view showing a configuration of thefirst bi-phase Scott-T transformer circuit 140 is shown in FIG. 1B. Asshown, the b-phase Scott-T transformer circuit 145 includes twotransformers (T1, T2) that are configured perpendicularly to each other,hence the “T” nomenclature. The first transformer (T1), which is the“main” transformer, consists of primary winding that is split between afirst section 202 and a second section 204 and a secondary winding 216.The second transformer (T2), which is the “teaser” transformer, consistsof a primary winding 208 and a secondary winding 210.

A first end 212 of the first second of primary winding 202 of the firsttransformer (T1) is coupled to a first phase (1)=0° of a three-phasepower supply. The second end of the first section 202 is connected tothe first end of the second section 204 by a conductor 215. A second endof the section 202 of the primary winding of the first transformer (T1)is coupled to a conductor 215 (e.g., an electrical wire) that connectsthe first section to second section 204. The second end 218 of thesecond section 204 is coupled to a second phase (Φ=120°) of athree-phase power supply. The first end 222 of the secondary winding 206of T1 is coupled to electrode 132 of the first electrode pair via ahigh-voltage entrance bushing. The phase of the signal provided to theelectrode is (Φ=90°), one phase of a two-phase system. A second end 224of the secondary winding 206 of the first transformer (T1) is grounded.

Turning to the second transformer (T2), the first end of the primarywinding 232 taps the center of the primary winding 208 of T1 (i.e.between sections 202, 204) in a 1:1 ratio. That is, 50 percent of thewindings of the primary of the first transformer (T1) are in section202, and 50 percent are in section 204. The second end 234 of theprimary winding 208 of transformer (T2) is coupled to a third phase(Φ=240°) of a three-phase power supply. The second end taps the primarywinding 208 of the second transformer (T2) is an 86.6% (0.5×√3) ratio.The first end 242 of the secondary winding 210 of the second transformer(T2) is the connected to electrode 134 of the first electrode pair via ahigh-voltage entrance bushing. The phase of the signal provided to theelectrode is (Φ=90°), the other phase of the two-phase system. A secondend 244 of the secondary winding 210 of the first transformer (T2) isgrounded.

The second transformer circuit 145 of the coalescer apparatus is coupledto the three-phase power supply and the second pair of electrodes136/138 in the same manner so that there is a symmetry between the waythe first and second electrode pairs 132/134, 136/138 are electricallyenergized.

In the configuration shown in FIG. 1B, the bi-phase Scott-T transformeris a step-up transformer and the secondary windings are at a highervoltage with respect to the primary windings. As noted, the first sidesof the secondary windings of the first and second transformers (T1),(T2) are connected to the inside electrodes inside the vessel 105 whilethe other sides are grounded. This configuration generates high-voltagetwo-phase power signal with the same voltage and a phase shift of 90degrees from a three-phase power supply. In each pair of electrodes132/134, 136/138, the top electrode is coupled to the (Φ=0°) phase whilethe bottom electrode is coupled to the (Φ=90°) phase. The normalizedpotential difference between the electrode is equivalent to sin x−cos x,which is another sinusoidal signal. This configuration generates a moreuniform and homogenous electrostatic field with same voltage density andno phase shift. In addition, in the embodiment of FIGS. 1A and 1B, onlytwo transformers need to be employed, in contrast to the conventionalthree-phase coalescer that uses three transformers.

FIG. 2A is a schematic cross-sectional view of the same embodiment ofthe coalescer shown in FIG. 1A but this figure shows the waveform ofvoltage intensity between the symmetric electrodes supplied by thedisclosed Scott-T transformer circuits. As shown, there is a first AChigh voltage waveform 305 that represents the voltage between the firstelectrode 132 and the second electrode of the first electrode pair ofthe coalescer. A second AC high voltage waveform 310 represents thevoltage between the first electrode 136 and the second electrode 138 ofthe second electrode pair. A similar pattern is generated between thebottom plates and the interface level that forms as water coalesces andseparates from the crude oil emulsion. This water then exits from thevessel via the water outlets 120, 122. Some of the soluble impuritiespresent in the original crude oil emulsion are removed with the water.

As illustrated, the waveforms 305, 310 have the same amplitude andphase, providing a uniform electric field throughout the coalescer. Theuniform field, in turn, creates homogeneous condition for theaggregation of water throughout the vessel, improving the efficiency ofthe coalescing process. FIG. 2B is an exemplary graph showing a voltagedensity between the electrodes (of each pair) over time. In variousimplements, voltage levels in the vessel can be maintained within arange of 15 Kilovolts to 25 Kilovolts which is suitable for inducingsufficient aggregation of water molecules to ensure their separationfrom the crude oil emulsion.

There are a number of advantages to the coalescer apparatus poweredusing bi-phase Scott-T transformers according to the present disclosure.The use of Scott-T Transformers for AC electrostatic coalescers reducesthe number of transformers required for each vessel to 2 from 3; by thismeasure, the possibility of unbalanced voltage on the primary windingsis reduced. The reduction of the possibility of unbalanced voltages, inturn, reduces power loses over time, avoids undesired voltage drops, andincreases transformer life. This will result in a more robust andresilient design with a power cable redundancy. In some embodiments, thetwo bi-phase Scott-T transformer circuits coupled to the vessel can beprovided with an independent power supply. Therefore, if one powersupply is lost, only one of the transformer circuits will be down andthe other one can keep working and provide a partial treatment of theemulsion, mitigating the upset. Importantly, the disclosed coalescerusing bi-phase Scott-T transformers enables the employment of symmetricelectrodes with a more uniform and synchronized (no phase shift)electrostatic field throughout the entire length of the vessel. Thismeasure improves water droplet aggregation (coalescing) and separation.

It is to be understood that any structural and functional detailsdisclosed herein are not to be interpreted as limiting the systems andmethods, but rather are provided as a representative embodiment and/orarrangement for teaching one skilled in the art one or more ways toimplement the methods.

It is to be further understood that like numerals in the drawingsrepresent like elements through the several figures, and that not allcomponents or steps described and illustrated with reference to thefigures are required for all embodiments or arrangements.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentdisclosure. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and “comprising”, when used in this specification, specifythe presence of stated features, integers, steps, operations, elements,or components, but do not preclude the presence or addition of one ormore other features, integers, steps, operations, elements, components,or groups thereof.

Terms of orientation are used herein merely for purposes of conventionand referencing and are not to be construed as limiting. However, it isrecognized these terms could be used with reference to a viewer.Accordingly, no limitations are implied or to be inferred.

Also, the phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having,” “containing,” “involving,” andvariations thereof herein, is meant to encompass the items listedthereafter and equivalents thereof as well as additional items.

The subject matter described above is provided by way of illustrationonly and should not be construed as limiting. Various modifications andchanges can be made to the subject matter described herein withoutfollowing the example embodiments and applications illustrated anddescribed, and without departing from the true spirit and scope of theinvention encompassed by the present disclosure, which is defined by theset of recitations in the following claims and by structures andfunctions or steps which are equivalent to these recitations.

What is claimed is:
 1. An electrostatic coalescer for separating waterfrom a crude oil emulsion comprising: a vessel housing having a cavity,an inlet for receiving a crude oil emulsion, at least one outlet foroutput water removed from the emulsion, and a further outlet forpurified crude oil; a first pair of electrodes positioned within thecavity of the vessel housing; a second pair of electrodes positionedadjacent to the first pair of electrodes within the cavity of the vesselhousing; a first Scott-T transformer circuit coupled to the first pairof electrodes, the first Scott-T transformer circuit receiving as aninput a 3-phase power supply and outputting a 2-phase high voltagesignal to the first pair of electrodes; and a second Scott-T transformercircuit coupled to the second pair of electrodes, the second Scott-Ttransformer circuit receiving as an input a 3-phase power supply andoutputting a 2-phase high voltage signal to the second pair ofelectrodes; wherein the 2-phase voltage signal generated between thefirst pair of electrodes by the first Scott-T transformer circuit is ofa same amplitude and phase as a voltage signal generated between thesecond pair of electrodes by the second Scott-T transformer circuit,whereby a uniform and synchronized electrostatic field is establishedthroughout the entire length of the vessel free of any phase shift inthe electrostatic field resulting in water droplet coalescing andseparation from the crude oil in the crude oil emulsion.
 2. Theelectrostatic coalescer of claim 1, wherein the electrodes in the firstpair and the electrodes in the second pair extend in a horizontalorientation.
 3. The electrostatic coalescer of claim 1, wherein: thefirst pair of electrodes includes an upper electrode and a lowerelectrode, the upper electrode receiving a signal from the firsttransformer circuit of a first phase and the lower electrode receiving asignal from the first transformer circuit of a second phase 90 degreesshifted with respect to the first phase; and the second pair ofelectrodes includes an upper electrode and a lower electrode, the upperelectrode receiving a signal from the second transformer circuit of afirst phase and the lower electrode receiving a signal from the secondtransformer circuit of a second phase 90 degrees shifted with respect tothe first phase.
 4. The electrostatic coalescer of claim 1, wherein thefirst and second Scott-T transformer circuits each include a maintransformer and a teaser transformer that taps the main transformer in a1:1 ratio.
 5. The electrostatic coalescer of claim 4, wherein the maintransformer includes a primary winding having a first end coupled to oneof the phases of the three-phase power supply, and a second end coupledto another of the phases of the three-phase power supply.
 6. Theelectrostatic coalescer of claim 4, wherein the main transformerincludes a secondary winding having a first end coupled to a first oneof the electrodes of the first or second pairs of electrodes, and asecond end coupled to ground.
 7. The electrostatic coalescer of claim 6,wherein the teaser transformer includes a secondary winding having afirst end coupled to a second one of the electrodes of the first orsecond pairs of electrodes, and a second end coupled to ground.
 8. Theelectrostatic coalescer of claim 1, wherein the voltage generated withinfirst and second pairs of electrodes is in a range of 15 Kilovolts to 25Kilovolts.